The present invention relates to an end seal assembly for sealing the end of a conduit or passageway carrying multiple conductors such as optical fibers or wires or a feedthrough for optical fibers or wires into an enclosure or through a bulkhead, for example. The end seal assembly is particularly designed for underwater or other high pressure applications.
Modern communications systems, particularly those employing optical fibers as conductors, often require means for passing said conductors sealably through high-pressure barriers such as instrumentation housings. One such means has been to provide rigid metal bores through which the conductors pass and into which they are sealably restrained by epoxy potting material. One drawback to using epoxy potted directly into metal bores is that the two materials have different bulk moduli and thermal expansion coefficients. As a result, cracking of the epoxy, or separation of the epoxy-metal interface often occurs with thermal and/or pressure cycling.
A particular subset of feed-through applications involves the common use of rigid tubes, or cables, to contain and protect fibers. These may be incorporated within more complex cables. Sometimes these tubes or cables contain multiple fibers. Some cables are simply empty except for the fibers. Others are filled with gel. Such cables or tubes are typically of small diameter ({fraction (1/10)} inch or so). In gel-filled cables, the gel will expand or contract from the ends of the tube under changing pressure and temperature if it is not sealed, which will strain the fibers and potentially cause them to bend or break.
The ends of conductor-bearing cables, in practice, are usually terminated to fiber management chambers associated with connectors or instrument/equipment canisters. It is generally desirable to physically isolate the inside of the cables from these enclosures, both to preclude the exchange of fluid/gel between them, and to prevent the migration of fiber from the tube to the enclosure or vice versa. However, this can be difficult to achieve in a small size cable carrying multiple, very fine fibers or wires.
In co-pending application Ser. No. 08/856,928 of Cairns et al., filed May 15, 197, an underwater bulkhead feedthrough assembly is described in which optical fibers or electrical wires are fed from the end of an underwater cable through a bulkhead into an enclosure or equipment housing. The cable end is coupled to one end of a connector body, and the individual fibers or wires extend through a bore in the body and a seal assembly within the body. This assembly is suitable for many applications, but is difficult to assemble for small tubes with closely packed fibers or wires.
It is an object of this invention to provide an epoxy feed through seal which is resistant to cracking and separation of the epoxy as a result of thermal and/or pressure cycling.
It is a further object of the present invention to provide a new and improved end seal assembly for tubular conduits carrying optical fibers or electrical wires, which will sealably cap off the conduit while allowing the fibers to pass through into an instrument housing or the like, the interior of the housing being of an unequal pressure with respect to the interior of the conduit.
A third object of the invention is to provide a miniature version of a conduit end seal having a size commensurate with the conduit diameter.
According to the present invention, a conduit end seal assembly is provided, which comprises an end seal for seating in a seat portion in a conduit carrying one or more conductors, the end seal having a second through bore through which the conductors (fibers or wires) extend, the through bore being filled with epoxy material bonded to the inner surface of the end seal through bore and to the wires or fibers, and the end seal being of a material having coefficients of thermal expansion and compressibility approximately equal to the respective thermal expansion and compressibility coefficients of the epoxy material.
In a preferred embodiment of the invention, the material of the end seal is a thermoplastic material such as glass fiber reinforced plastic which has a coefficient of thermal expansion and a bulk modulus similar to that of the epoxy material filling the through bore and surrounding the fibers. The end seal is not necessarily a tight or sealing fit in the seat portion, and one or more resilient seal members may be mounted between the end seal and seat portion to provide a seal. The resilient seal member will compensate for any differences in thermal expansion or contraction between the seal body and end seal.
This arrangement avoids the problem of potential loss of the seal as a result of thermal shock or pressure cycling with subsequent separation between epoxy and metal surfaces. The provision of an end seal between the metal and epoxy, with the seal being of a material having a coefficient of thermal expansion and a compressivity substantially equal to that of the epoxy, ensures that the epoxy does not separate from the inner surface of the bore in the end seal. At the same time, the resilient seal member between the outer surface of the end seal and the seat portion will accommodate any difference in thermal or pressure induced expansion or contraction between the end seal and the metal seal body, ensuring an effective seal.